This invention relates to wavelength locking and output power control systems relative to multiple WDM signal channels and more particularly to such signal channels as found in a monolithic transmitter photonic integrated circuit (TxPIC) chip having a plurality of integrated signal channels with each channel having a modulated source.
There are many feedback loop systems known for controlling the wavelength of an array of lasers, particularly discrete lasers or so called EMLs employed in an optical transmitter for use in an optical transport network. Also, there are feedback loop systems to control the output level of modulated signals produced in such transmitters so that their power levels are equal across the array of signal channel generators. This power equalization is also referred to in the art as pre-emphasis. A characteristic of a monolithic TxPIC with an integrated multiplexer is that the light that emerges from the TxPIC already combines a plurality of data-modulated optical wavelengths. While advantageous for reliability and reduction of cost, this integrated multiplexing function poses challenges for control of individual optical wavelengths and channel average powers, as the information required to control individual channel powers and wavelengths must be extracted from the optical multiplexed signal at the output of the TxPIC.
What is needed is a control system that can concurrently control emission wavelengths and powers on such an array of lasers and more particularly on an array of integrated lasers or modulated sources in a transmitter photonic integrated circuit (TxPIC) with an integrated optical multiplexer. The control system can advantageously employ integrated channel active elements to aid in such emission wavelength and signal output power control.